1 - History. Include size/volume of aquarium or pond.

Husbandry eg.is it filtered?If so then is it undergravel only; electric powerfilters;Ultra-violet filtration units (used to control suspended algae in ponds and reduce pathogen levels, but the tubes are relatively short-lived and need regular changing to maintain maximum effect, plus if used on large ponds I doubt very much their efficacy at the latter).

Stocking levels - see OFI guidelines.

Frequency and extent of water changes (little and often usually better than less frequent but major and therefore potentially stressful changes).

2 - Are several fish involved?

If NO, consider individual problems.

If YES, consider environmental problems e.g.water quality.If only certain species are affected consider specific predispositions eg.the small Gastromyzon loaches inhabit fast flowing, cool mountain rivers and so their Hb has a reduced O2 affinity making them difficult to keep in most aquaria.

3 - If more than one species is affected, then check water quality parameters.Where possible check:

NH3

Redox potential (marine only).

4 - If there are water quality anomalies, then address these. If there are no problems there, assess other factors that impinge on the pond/aquarium.eg.pesticides/herbicides (slug pellets as fish food!), smoking. Nutritional deficiencies are rare when fish are fed commercial diets, but can occur if fed "fresh" foods.

5 - If the answers to all the above are NO, and one or more fish are affected move on to a physical examination. Assess:

Demeanour - are the fish "depressed" or active? Do they swim on a even keel?Do they shoal with the rest (if applicable) or do they stay by themselves.

Fins - are they upright, or clamped against the body.Check for signs of tearing, erosion or haemorrhage.

Colour - are the colours bright, or dulled (often as a result of excess mucus production secondary to external parasitism).

Stress will often cause a change in colour especially in certain varieties of koi.

Condition - are the fish a normal shape for their species or are they thin, eg.young koi with Bothriocephalus infestation.

Integumentary lesions.Haemorrhages or ulcers typical of aeromonas infections in koi and goldfish.Fibrosarcomas in goldfish or dermocystidium in koi. Any large external parasites such as Argulus.

Respiration.Is the respiratory rate increased, with the operculae extended.Look for strings of mucus coming from the gills.Do the fish hang at the surface, gulping at air or congregating around filter outlets or fountains where there is maximum oxygenation of the water?

Faeces. Are the faeces normal, or stringy as in cappilarial or hexamita infestations in discus. If size of the fish allows, consider giving a GA (or possibly euthanase and postmortem) to allow:-

Mucus scrapes.(ext.parasites)

Swabs for bacteriology

Coelomic taps

Biopsies eg gills

Blood samples (Caudal vein)

Radiography

Ultrasonography

Faecal examination.

And if fish is a postmortem, then :

Swabs from visceral lesions

Tissues for histopathology.

6 - If nothing is identified, reassess.

NB: Response to treatment is an important part of diagnosis.

NB2: Many diseases are not yet curable.

Anaesthetics.

MS222 - Water soluble powder.Can be irritant because causes a fall in pH as it dissolves.

Benzocaine.Not water soluble therefore must be dissolved in either ethanol or acetone first. Not as safe in my opinion.Because these anaesthetics are fat soluble, and the metabolic rate of the anaesthetised fish depends on several variables eg. water temperature as they are ectotherms, large fish can have marked recovery times.

Treatments :

Medications are administered to fish by a variety of routes, namely:

a) By mouth. Antibiotic medicated food is available either as flakes or pellets.Usually either oxytetracycline (resistance prevalent) or oxolinic acid (occasional resistance problems).Pellets or flake.Antibiotic leaching out of uneaten food can affect biological filtration therefore monitor NH3 and NO2 levels. Some people adminster drugs by gavage (stomach tube)(use Jackson's cat catheter). Goldfish and koi do not have a stomach therefore gavage may give unpredicable results.

b) By bath.Can be stressful, but at least main aquarium/pond not exposed to drugs.

c) Directly into aquarium/pond water.Risks to biological filtration. Also many ponds difficult to assess true volume for accurate dosing.

d) By injection. More accurate and specific.Stressful and limited by size of fish.Prefered sites :

Dorsally, immediately anterior to the dorsal fin, inject "between the fillets".Well absorbed, but in very visible area in pond fish eg.koi.

Pectoral musculature.Feasable in large fish only.

Intracoelomic.Risky eg.in koi and goldfish all organs adhered together so very easy to pierce organs.

Tail muscles.Easily accessable but arrangement of myomeres tends to squeeze some of drug back out through injection hole.

Zoonoses.Most important one is mycobacteriosis (Fish TB).Usually M.fortuitum and M.marinum.Low temperature adapted so usually cause superficial granulomata, but occasionally will track up lymphatics. Aeromonas, pseudomonas and edwardsiella have all been recorded in immuno-compromised patients.Leptospira icterohaemorrhagica (Wiels Disease) is a theoretical risk when working near ponds visited by rats. Some fish are venomous eg.lionfish (Pterois sp.) whilst others can deliver a nasty bite eg trigger fish.

Always take the time to examine any dead fish, even if the cause of death is known. There is no substitute for familiarity with your target species. The first step in diagnosing disease is the ability to distinguish normality from abnormality, to become familiar with the spectrum of what one should expect to find, and recognise what is outside of this. For example, the ovaries can vary tremendously in size depending upon the age and the sexual state of the individual fish, yet one must learn to tell the difference between these wide ranges of 'normal', and disease such as egg retention with necrosis (tissue death) and secondary infection, or neoplasia (tumours). If dealing with paired organs such as the gonads (reproductive organs) or kidneys a useful tip to remember is that fish are largely symmetrical so comparison of left and right sides can be useful in determining which side is swollen (or shrunken!). It is not just relative size that is important, but other qualities may prove useful such as colour and texture - many fish have a black lining to the coelomic (body) cavity, or the liver may naturally have blackened areas of pigmentation. These should not be construed as abnormal. In albino varieties they may be (naturally!) absent however. The process of autolysis (decompositon) starts very rapidly in fish, especially in warmer waters. This causes changes in the colour and textures of many organs such as the liver which may pale or develop a mottled appearance. These are normal degenerative changes and need to be distinguished from disease. Fatty livers are often pale and tear easily. Therefore ideally post-mortems are performed immediately following the humane euthanasia of suspect fish.

Because fish cadavers deteriorate so quickly, there is a rapid overgrowth of environmental bacteria as contaminants. These bacteria may migrate through the blood or tissue fluid only to be isolated on bacteriology and possibly mistaken for septicaemic/bacteraemic pathogens. An easy mistake to make as many of the common fish pathogens are also present in their immediate surroundings. Therefore any fish presented which has been dead for greater than 12 hours will be of only limited use. Dead fish for post-mortem should be kept cool (around 4C) prior to examination. This, plus a suitable sterile post-mortem technique should reduce the risk of such a mistake. Freezing of the cadaver is not suitable as ice crystals disrupt the cellular structure of the internal organs making them unsuitable for histopathology.

A further point to remember is that the handling of fish material does expose the handler to certain risks either from the water the fish is in eg. Leptospira, or from the sample tissues themselves eg. the Fish Mycobacteria - M. marinum and M. fortuitum. A sterile technique and attention to basic hygiene procedues eg. wearing gloves and covering cuts and abraisions will drammatically reduce the risks involved.

When considering fish disease, a holistic approach is necessary . Fish are in such intimate contact with their environment that one must ALWAYS assess any fish disease or mortalities in conjunction with water quality assaysand other environmental features. Stress, and consequent immune suppresion is probably the commonest underlying cause of disease in fish.

1 - External Examination. Many clues as to the state of certain internal structures can be ascertained by a critical external examination eg. internal tumours may give rise to asymmetric swellings of the body cavity, or Mycobacterial infections can result in collapse of vertebrae giving rise to fish with kinked spines. A pinecone appearance is due to ascites, a build up of fluid in the coelomic cavity as a result of osmoregulation imbalance from severe renal or gill disease.

2 - Faecal examination. Colour and consistancy may vary with disease. Examine faeces microscopically with a light microscope for worm eggs eg. Capillaria, or Protozoa eg. Eimeria. Bacterial swabs are probably best taken from within the rectum to reduce the risk of contamination.

3 - Catheterisation of the urogenital oriface can be useful to assess sperm or ovum quality eg. in large koi.

Post-mortem Examination.

Before examining the coelomic cavity, the external surfaces should be steralised to reduce the risk of introducing contamination. This is best achieved by dipping in, or applying 70% alcohol (surgical spirit) to the outside of the fish. The fish is then laid, if possible, on its left side on a non-slip surface.

Using a sterile pair of fine scissors and forceps two incisions are made. Both start from the operculum (gill cover), but one moves dorsally (upwards) towards the spine and then follows the contours of the body cavity paralell to the spinal column and then ventrally (downwards) to the anus, whilst the second cut is midline along the belly of the fish again to the anus where the two incisions meet. This should allow the right wall of the coelomic cavity to be removed. Assess the type and character of any coelomic fluid present and collect with a sterile syringe and needle if required. Watch out for any adhesions (areas of attachment) of organs to the inside surface of the body cavity as these may be due to areas of inflammation. Most of the internal organs should now be exposed. It is normal for the organs of Koi and Goldfish to be tightly adhered to each other.

One should now set about identifying the main structures:-

The swimbladder, if present, is usually a large, silvery organ lying along the dorsal boundary of the coelomic cavity. It may appear as a single organ eg. Trout, have an anterior/posterior divide eg. Goldfish , or appear in three sections eg. sucking Catfish (Loricaridae).

Immediately dorsal to the swimbladder lie the dark red kidneys, and immediately below it are the gonads. The kidneys may be divided into cranial and caudal halves.

The intestines are usually very obvious ventrally. The length of gut will vary from species to species, with herbivorous fish having relatively long intestines, often arranged into coils, whereas carnivorous species usually have a relatively large stomach and a short gut length. If a spleen is present it is often hidden within the intestinal mass.

The liver occupies the anterior border of the coelomic cavity and is a sizable organ. Usually a deep red, it colour can vary depending upon other factors eg fatty diet or vitellogenesis. In Sharks it is a very large organ which has a role in buoyancy.

The heart lies immediately anterior to the liver , often at the level of and between the pectoral fins (pectoral girdle).

Having assessed the internal organs for any obvious abnormality, either physical or positional, then the whole of the gastrointestinal tract is removed (including the liver). This is achieved by cutting through the oesophagus proximally, and through the rectum as close to the anus as possible distally. If there is a risk of escape of gut contents then these should be ties off prior to removal.

The liver is usually a dark red/tan colour, although its colour can vary. The edges should be sharp, not rounded. Several incisions should be made into the substance of the liver to examine for parasites or obvious lesions. Any discoloured or raised areas should be retained for histopathology (see later).

Usually associated with the liver is the gallbladder. This contains bile which is usually a yellow to dark green colour. Fish which have been dead awhile may show staining of the surrounding tissues with bile. If the fish has not fed for some time the gallbladder can be quite distended. The bile can be collected with a syringe for examination for protozoa or frozen for toxicological analysis.

The spleen is a flat, triangular dark red organ usually positioned close to the stomach. However it may not be immediately obvious as it is often hidden in fat or by loops of gut. If the spleen is obviously swollen it should be cultured , or touch preparations performed (see later).

The guts are placed to one side to reduce the risk of accidental contamination of the other organs.

Returning to the coelomic cavity the sex organs should be removed. Fish which are not sexually active may have insignificant gonads. As a general rule immature but developing eggs are greenish, whilst mature eggs are yellow - there can be marked differences between species however. Brown, black and obviously degenerating eggs can be a sign of egg retention. Mature testes in males are usually large, firm and white. Smearing the cut surface of testes on to a slide may help one to gain an idea of sperm motility.

The swimbladder should now be examined. Some fish such as Carp have a direct connection between the swimbladder and the oesophagus (physostomes). This connection is called the pneumatic duct and with care can be often be visualised. Look for any abnormalities or blockages. In other species there is no connection (pysoclistous). Such fish show obvious retia mirabilia which are an often circular patch(es) of blood vessels on the surface of the swimbladder. Look for any signs of haemorrhage on the surface, or exudates inside one or more chambers.

The kidneys can be removed next. These are important as bacteria tend to localise here in large numbers in cases of septicaemia. Touch preparations and bacterial culture are recommended. In those species with divided kidneys sample from both sections. In some species a urinary bladder may be present at the point of fusion between the two ducts from the kidneys. Unfortunately the kidneys are often easily damaged and so for histopathology, a dorsal wedge is taken. This involves taking a section of kidney, spinal column and dorsal musculature by incising dorsally from the abdomen up towards the back of the fish.

The heart can now be examined. Look for an increased amount of fluid around the heart, as well as any obvious lesions, haemorrhages or raised areas. Sever the cranial and caudal connections. If the heart is large then incise it along its length to examine the internal surface and the valves.

Several incisions should be made into the muscle blocks of the fish to look for lesions such as parasitic metacercaria. Note the colour and texture of the muscle, especially for any signs of wasting.

Skin samples can be taken for histopathology if required. If there is an obvious skin lesion eg. an ulcer then make sure to include some healthy normal tissue surrounding it in the sample. Also try to submit samples which include sections of the lateral line.

If the fish has shown nervous signs or it is otherwise felt necessary to examine the brain, this can be done by removing a section of the skull immediately above the eyes. The brain is easily damaged during this process especially if one is having to make a hole in a heavily armoured skull such as a Phractocephalus catfish. In this situation remove the head/skull and make small holes into the skull cavity before placing the whole into formal saline. In this way the brain is preserved and firmed by the preservative and can either be subsequently easily removed, or sectioned in situ. The brain deteriorates very quickly so its examination is only suitable in very fresh specimens.

Now return to the guts. Examine for any abnormalities such as raised areas or haemorrhages on the outside (serosal) surface. The stomach and if possible the entire length of the bowel are opened and examined for parasites and obvious lesions. If food is present try to identify it. Sections of the stomach, intestine and colon should be submitted for histopathology.

Sample collection.

i - Viral. If virus isolation is required, then transfer of sample tissue to an appropriate Viral Transport Media, and kept at around 4C is best. Normal histopathological techniques may show the presence of certain viruses eg. adenoviruses or herpesviruses.

ii - Bacterial. Bacteriological samples can be taken either with swabs or sterile loops. The external surface of the organ is first seared, then an incision is made into the organ with a sterile scalpel blade or scissors. The loop/swab is introduced. If samples are to be forwarded to laboratories, then Bacterial Transport Media is recommended. Some bacteria are difficult to culture routinely eg. Mycobacteria. These are more likely to be diagnosed from histopathological sections or needle aspirates, with special staining techniques.

iii - Chlamydial. Suspect samples should be transferred to a suitable Chlamydial transport medium. Chlamydia can be demonstrated with histopathology.

iv - Fungal. Same principles as for Bacterial samples. Some fungi eg. Ichthyophonus are diagnosed primarily with histopathology.

v - Parasitic.

a - Macroparasites eg. helminths, can be teased free and removed in toto, or with part of the organ at the point of attachment.

b - Microparasites eg. Protozoa. Best diagnosed in situ with histopathology eg. Hoferellus carassii.

vi - Histopathology. Sections of tissue are preserved in formal saline as a fixative for histopathological examination. In all cases try to include some adjacent healthy tissue in the sample taken. Relatively small pieces are more than adequate for the majority of samples. Care should be taken to ensure samples are placed into relatively large volumes of formal saline (roughly 1:10), plus if brain is to be preserved, open skull to allow fixative access.

vii - Touch Preparations. Samples of tissues have a cut surface briefly dabbed on to a clean glass slide. These slides are then stained and examined microscopically. This technique gives information on cell types present and certain pathogens eg. bacteria (although this is of very little use in identifying the species of bacteria).

viii - Toxicology. Samples required and how they are to be handled vary with which toxin one is looking for, therefore I would advise that you discuss what you require with the laboratory first.

Temperature requirements are species specific for tropical freshwater fish, although temperatures of around 25C are usually provided. At temperatures outside of the optimum range, certain aspects of metabolism may be affected including the immune system, digestion and drug absorption and utilization. At temperatures above this range fish will become stressed, partially as a result of oxygen depletion.

OXYGEN LEVELS O2 concentration in freshwater at 25C is around 6.0ppm, whereas at 30C it has fallen to 5.6ppm. 5.0ppm is considered as a minimum safe concentration so there is very little safety margin. If in addition to high temperatures, there is little or no circulation, poorly maintained filtration and excess organic material in the tank, O2 levels can fall to dangerous levels. Affected fish will be seen at the surface, head uppermost and with a high respiratory rate. The situation can be alleviated by improving gaseous exchange at the water surface by increasing aeration/circulation, removing mulm from the tank and inproving filtration maintenance. The installation of "trickle" filtration will reduce the demand for dissolved O2 by the bacterial filter flora.

A heavily planted aquarium can be problematic. While the lights are on, photosynthesis occurs and, as a by-product, O2 is liberated into the surrounding water. In extreme circumstances the water can become supersaturated with O2 giving rise to "gas bubble disease" where bubbles of O2 are obviously apparent in the vessels of the fins, skin and occasionally behind the eyeball. Again, increasing the opportunities for gaseous exchange by improved circulation will rectify the situation, allowing the excess O2 to disipate. During the hours of darkness, no photosynthesis occurs but the plants still respire and so compete with the fish and filter bacteria for available O2.

pH As a general rule a pH of around 7.0 to 7.5 is accepted by most fish. Some species such as discus (Symphysodon sp.) prefer more acidic conditions (6.5 to 7.0) whilst others, such as the African Rift Lake species, prefer a higher pH of around 8.0 to 8.3. One of the main points to remember about the pH scale is that it is logarithmic, such that each point represents a ten-fold difference from that of the next. Therefore a pH change from 5.0 to 7.0 is a 100-fold change. Rapid pH changes can be stressful, with effects on osmoregulation and respiration. In an established aquarium the pH will tend to fall due to a gradual accumulation of organic acids, plus CO2 production from bacterial beds, fish and plants. Below pH 6.0 the bacterial filter beds are compromised and total ammonia levels can quickly rise to toxic levels. Also fish may show signs of acidosis - frantic movements, bleached colouration, skin haemorrhages and coughing.Treatment involves correcting the pH slowly, with partial water changes and suitable buffers; the situation can be avoided by regular monitoring of pH.

HARDNESS This is a measure of the dissolved salts, especially those of Ca++ and Mg++, present in the aquarium water. Soft water has less salts than hard. Sudden changes in hardness can be stressful.

NITRIFICATION Problems can arise with new, or inadequate biological filtration, or in systems subjected to low pH or medication as significant levels of total ammonia can result. Antibiotics in aquarium will kill off the beneficial bacteria as well as the pathogenic species. Dissolved ammonia exists as an equilibrium between two forms, the ionised NH4+, and the free, non-ionised NH3. Their relative proportion depends upon the ambient temperature and pH. A rising pH, or an increase in temperature produce an increase in the non-ionised NH3. This is considered the more toxic form as it is able to cross cell membranes and can result in an encephalopathy. NH3 is also considered to be irritant, especially to the skin and the fragile gill membranes (if chronic then a secondary gill hyperplasia can result). Affected fish show an increase in cutaneous mucus production and cough due to the irritation. High levels of NO2 cause a significant oxidation of the haemoglobin in the RBCs to form the stable compound methaemoglobin. Affected fish become hypoxic and can die. Increasing oxygenation will have no effect. Discus can show signs of NO2 toxicity at levels as low as 0.5ppm.If diagnosed the addition of either cooking salt or aquarium salt (not table salt) to the water will help as the chloride ions appear to competetively inhibit the transport of NO2- ions across the gill membrane into the blood stream. NO3 is less toxic than NO2, but prolonged exposure to NO3 may be stressful and hence immunosuppressive.Remedial action is by water changes, and by correcting the underlying problems eg improving filtration or reducing stocking levels.

Nutritional diseases are rare as there are some very good proprietary foods available.

VIRAL DISEASES Certainly there are a great many viruses affecting tropical freshwater fish - for instance angelfish (Pterophyllum sp) have been found to harbour paramyxoviruses, herpesviruses, parvoviruses and adenoviruses. However few specific disease entities have been ascribed to the majority of viruses isolated. One obvious viral disease is lymphocystis, an iridovirus, which causes gross hyperplasia of the dermal fibroblasts to form large, whitish masses typically on the fins.Infection is usually selflimiting and will resolve spontaneously.Ultra violet sterilization will help to control the spread of water bourne viruses.

BACTERIAL DISEASES Usual pathogens are aeromonas, pseudomonas and flavobacteria.These are environmental contaminants and are usually secondary invaders of otherwise stressed fish.Classical signs are altered colouration, frayed fins, haemorrhages and ulceration, weight loss and anorexia.Cytophaga-like bacteria such as flexibacter, can be the cause of "mouth fungus" (especially seen in livebearers) and fin rot.Fish mycobacteriosis (Fish TB) commonly due to M.marinum, M.fortuitum or Nocardia, can present with a wide variety of signs such as chronic weight loss, exophthalmia, skin lesions and spinal deformities. Fish with gill hyperplasia, such as seen with chronic ammonia exposure may subsequently suffer secondary bacterial or fungal infections.The gill filaments are often so inflamed and swollen that the operculi are unable to close. The respiratory rate will be high.Treatment is with appropriate antibiotcs - consider enrofloxin (Baytril) either by injection at around 10mg/kg bodyweight e.o.d. or as a bath at 30ppm for 1 hour daily for 5 days.If feeding, oxolinic acid medicated food should be considered. Where possible always consider doing bacteriology and sensitivity tests because of increasing resistance to eg oxolinic acid. Chloramine-T can be beneficial with gill disease, but lower concentrations required in soft water.

ENDOPARASITES Nematodes, especially Camallanus which has a direct and indirect life cycle can occasionally cause problems. Usually introduced with live aquatic foods such as tubifex worms, numbers can build up rapidly in aquaria.Some fish will appear to bulge they carry so many worms.Diagnosed by typical ascarid eggs in faeces, or at post-mortem. Capillaria can be a problem in discus - signs include mucoid faeces and weight loss. Typical Capillarial eggs in faeces. Cestodes are usually of little significance in aquaria. The typical indirect lifecycles of these parasites cannot be sustained in captivity. Occasinally encysted stages in the muscle or body cavity may need attending to.

Hexamita - putative cause of "Hole in the Head" disease seen in cichlids such as discus or oscars. Normally an intestinal parasite this flagellate can invade liver, gall bladder and heart. Affected fish fail to thrive, lose weight and become anorectic. Concave ulcerative lesions appear anteriorly, and progress along the lateral line. These lesions may trail a string of mucus (these may occasionally be mistaken for worms). These lesions are associated with Hexamita, but interestingly are often free of the parasite. Often secondary to stress, further manifestations include high fry mortality, poor egg hatchability and reduced reproductive performance. The organism can be demonstrated in faeces of body fluid. The related flagellate Spironucleus can cause disease in angelfish (Pterophyllum).Plistophora is a microsporidean parasite of the muscles of tetras and related fish (it was originally known as Neon Tetra Disease). Affected fish show a paling colouration and eventually physical deformity due to muscle wastage. There is no cure.

ECTOPARASITES Protozoa are numerically the most important external parasites. The most familiar is White Spot, caused by Icthyophthirius multifilis. It is the free swimming stages of this parasite that are the most susceptible to treatment.Higher temperatures speed up the life cycle thereby exposing the susceptible stages sooner. Very quickly eradicated with proprietary White Spot medications. Vaccination may be a future possibility. Other ciliate protozoan parasites include Chilonodella,Trichodina and Tetrahymena. In large numbers they are intensely irritant, stressing the fish and predisposing to secondary infections.Again commercially available medications or glacial acetic acid dips should suffice.Oodinium (Amyloodinium) is the cause of Velvet or Rust disease.Parasitic for only part of its life cycle, numbers can build up in aquaria such that newly introduced fish can die within 12 hours.Infested fish show lethargy, loss of appetite, flicking,loss of normal colouration and unco-ordinated, darting movements. Respiratory distress is common as the gills are preferentially targeted. Affected fish often have a yellowish, dusty appearance. Treat with metronidazole or quinine hydrochloride, or a proprietary copper based medication. Remember copper can be toxic therefore monitor with test kit. Icthyobodo (Costia) necatrix is considered a normal skin inhabitant helping to remove sloughed tissue and mucus.If fish are immunocompromised, then numbers of Icthyobodo increase; affected fish are depressed, with fins clamped but usually continue to feed. The usual ciliate treatments will suffice.

Monogenean trematodes (Flukes). The skin fluke (Gyrodactylus) may be irritant if present in large numbers. This is a livebearing fluke and so is relatively easy to control. The gill fluke,Dactylogyrus, can be a source of serious disease, both directly by damaging the gill lamellae, and indirectly by allowing secondary infections to establish. In addition there is a relatively resistant egg stage. Treat with organophosphorus compounds such as dichlorvos.Also useful is praziquantel or the benzimidazole compounds.

FUNGAL DISEASES Usually secondary invaders. Spores common in aquatic environments. Usually Saprolegnia, others are occasionally seen. Topical treatments with povidone-iodine daily, or baths in malachite green or phenoxyethanol.Occasionally Branchiomyces may be isolated from necrotic looking gills - hence its name of gill rot. Ichthyophonus - a systemic and as untreatable infection, may be seen.Affected fish show signs similar to fish Mycobacteriosis.

Occasionally encountered. In some species may be viral induced eg. in fish of the xiphophorus genus (swordtails and platies) the melanomas and neuroblastomas seen, seem to be due to a papovavirus and two retroviruses respectively. Differential diagnoses include Lymphocystis virus, and parasitic cysts.

CONGENITAL/HEREDITARY ABNORMALITIES.

May be encountered, and occasionally used by breeders to develop new varieties!

TOXINS Not only as a result of poor water quality, but consider heavy metal contamination (lead pipes), fly sprays and cigarette smoke.

As a general rule the oceans are an extremely stable environment and so aside from boundary zones such as rockpools, estuaries, and mangrove swamps, daily and even seasonal variations in water quality and temperature are limited. It is because of this that many marine organisms appear to have only a limited ability to respond and adapt to major alterations in their environment, primarily because there has been no evolutionary pressure to develop these. When we transfer such creatures from their native habitats to aquaria everything must therefore be perfect - there is little room for error. Unfortunately there are problems with the maintenance of the home marine aquarium. Consider:-

1 - Water quality. Saltwater holds less oxygen than freshwater,increasing the risk of overstocking. The pH of is usually high, around 8.3. At this high pH ammonia is in the toxic NH3 form; the normal biological processes occurring in the aquarium tend to lower the pH, reducing the buffering capacity of the water possibly to a dangerous extreme.

2 - Many reef fish such as the damsels and angelfish are territorial, vigorously defending either an individual or a pair's territory against all other fish, especially conspecifics. This behaviour, essential on a highly populated reef, may cause problems in the confines of small aquaria, stressing not only the other tank inhabitants, but also the territorial individuals themselves who will be unable to drive the "interlopers" from their territory. An alternative lifestyle is that of shoaling where the fish congregate in large schools thereby reducing the chances of an individual being predated, but also helping to maximise the use of certain food resources and to increase the opportunity for male-female interactions for spawning. A classic example of these would be the Anthias species. However due to the low stocking densities of marine aquaria, the relatively high price of individual fish, and the tendency for many aquarists to want "one of each" these fish are rarely kept in the correct social numbers or groupings.

3 - The vast majority of marine fish and invertebrates are wild caught. This means that they all come with a certain amount of baggage in the form of parasites, bacteria, viruses and the like which all wild fish carry and live in balance with. If we take all the above into consideration we can see that there is a recipe for disaster. If one buys an apparently perfectly healthy fish, if it is wild caught one must assume that it will be carrying something somewhere and there is little that can be done about it - certain treatments actually cause problems such as penicillins inducing blindness in clownfish, whilst many diseases have no known cure as yet. What we have got some control over is the environment within the aquarium. With correct husbandry techniques we can maintain the water quality at its optimum, feed the right foods and provide the correct social environment such that the fish are able to function at their best and will be able to control any pathogens with their own immune systems.

ENVIRONMENTAL DISORDERS.

Temperature. This should be as close to the fishes' natural environment as possible. Fish (and invertebrates) are ectotherms reliant upon heat from their surroundings to support their metabolic processes. At low temperatures their immune systems are compromised, as are other processes such as their metabolism, digestion and drug absorption.Excessive high temperatures will reduce the oxygen holding capacity of the water and stress the fish.

Salinity.The water surrounding a marine fish is more concentrated than the body fluids of the fish and so osmosis constantly draws water from the fish. To prevent dehydration, saltwater fish must drink, with the salt that they imbibe being excreted via the mucus secreting glands of the skin,in the faeces, but primarily from the kidneys and the gills. Sudden alterations in the salinity of the water will drammatically upset this delicate balance stressing or even killing the animal.

Oxygen level. The amount of dissolved oxygen is determined by the atmospheric pressure, the temperature and the salinity.Increased temperature or salinity will reduce oxygen levels, often to dangerous levels.

pH.Saltwater has a pH of around 8.0 to 8.3, and has a significant intrinsic buffering capacity backed up by other calcium or magnesium carbonate containing aquarium furniture such as coral sand or dolomite. However CO2 and other metabolic biproducts from the aquarium inhabitants will tend to reduce the pH. This will to some extent be resisted by the normal buffering mechanisms but these can be exhausted allowing a rapid fall in pH. High levels of phosphates complicate this further by forming layers of mineral apatite over magnesium and calcium carbonate substances such as dolomite. Once this apatite is formed the substance is no longer able to exchange ions with the water and so its buffering ability is gone. In tanks with a heavy algal growth, during thew period of illumination the opposite may occur where all the available CO2 is utilised; bicarbonates are then used for photosynthesis resulting in the precipitation of carbonates and a rise in pH, often up to as high as 10.

Environmental Toxins. These include ammonia, nitrite, heavy metals, chlorine, chloramine and nicotine (cigarette smoke).Ammonia is particularly important because at the high pH of marine aquaria it is mostly in the more toxic form of NH3. Should one be correcting after a fall in pH, bear this in mind because as you raise the pH a significant amount of ammonia present will convert to the toxic NH3. Of the heavy metals, copper is probably the most important because it is toxic to invertebrates at low concentrations and to fish at higher concentrations, yet it is an important constituent of many off the shelf medications. Copper can bind to rockwork in the aquarium, only to be slowly released at a later date, a fact which can result in invertebrate die-offs some time after copper containing medications were last used. Fortunately copper test kits are readily available.

Viruses appear to be very common in fish although not all are associated with disease. Treatment is rarely practical aside from provision of optimum conditions to allow the fishes' own immune system to deal with the infection. UV sterilizers may be used to destroy viral particles free in the water thereby reducing the risk of infection to other tank inhabitants.

Lymphocyctis virus. This virus induces massive cells to form which appear grossly as greyish-white masses on the fins and gills. Such abnormal cells may also be found in the muscle and body cavity. May be confused with chlamydial infections (epitheliocystis), parasitic cysts or sarcomas Infections are usually self-limiting and will spontaneously clear of their own accord.

Tang Fingerprint Disease. Oval fingerprint-like areas of discolouration occur on the sides of tangs and surgeonfish. Fish feed well at first but deaths can occur. Given ideal conditions the disease appears to be self-limiting. Initially thought to be a result of traumatic damage, microscopic investigations failed to confirm this; it is believed to be viral although no viral particles have yet to be identified.

Infectious Pancreatic Necrosis Virus. Usually considered a disease of salmonids IPN virus (or to be precise, a virus indistinguishable from IPN) has caused disease in over twenty different species of tropical marine fish. Affected fish die very quickly. In an outbreak the fish lost appetite, became lethargic and eventually disorientated. Some became ascitic and haemorrhages at the base of the fins were common. Unlike in salmon there was none of the classic necrosis of the pancreas.

Angelfish Encephalitis. Seen in French and gray angelfish, affected fish become lethargic, lose their appetite and secrete excess mucus. Eventually they lose their balance and die. There is no known treatment or control measures.

"Hole in the Head" disease of angelfish. Head and lateral line erosions seen in marine angelfish. Associated with an aquariovirus.

Most bacterial diseases of marine fish are secondary opportunist infections, secondary to such stressors as poor water conditions, temperature fluctuations and transportation.

Vibriosis. A rapidly progressing septicaemic infection characterised by skin haemorrhages, lethargy, anorexia and the eventual formation of deep skin and muscle ulceration. Definitive diagnosis and treatment is based upon culture and sensitivity tests. A commercial vaccine, produced for salmonids, is available and would be worth considering if Vibrio became a recurring problem.

Pasteurellosis. This presents as a haemorrhagic septicaemia similar to vibriosis. Should the fish survive this then grayish-white granulomatous lesions form in the spleen, liver and kidneys - a condition known as pseudotuberculosis. Treatment is with appropriate antibiotics.

Fish Tuberculosis. Very common in marine fish. Granulomatous lesions due to the mycobacteria can affect any organ and so the fish may present with emaciation, ulceration, anorexia, loss of colour, respiratory distress or exophthalmia. Laboratory diagnosis is essential especially because of the potential risk to the aquarist. Other bacteria may occasionally be isolated including Edwardsiella, Aeromonas, Pseudomonas, Streptococcus, Flexibacter or even Eubacterium tarantellus - this latter bacterium affects the central nervous system causing altered pigmentation and swimming patterns.

Epitheliocystis. This chlamydial disorder produces grayish masses similar to Lymphocystis virus, but can be tentatively differentiated from it by the fact that epitheliocystis usually affects the gills and only occasionally the skin. As the disease developes respiratory distress and death occur.

In marine fish fungal diseases are sporadic, the fungi usually acting as secondary invaders of wounds, or following stress or antibiotic medication.

Ichthyophonus. An internal disease, fish often become infected after ingesting affected fish. Whitish granulomas form in the internal organs; these may also be visable at the skin, which may also show signs of discolouration. Affected fish may show cork-screw swimming patterns or other abnormal coordination.

Exophialiosis. Also known as seahorse disease.It appears as non-ulcerative raised skin lesions. Similar internal lesions also occur especially in the liver. Affected fish are lethargic and often disorientated. There is no known cure.

Cryptocaryon irritans. Usually billed as the marine equivalent of whitespot, the disease usually presents itself initially by causing a loss of appetite, some skin irritation and minor respiratory distress. Closer investigation will reveal pinhead-sized white to gray nodules. The parasite causes excessive irritation resulting in exuberant mucus production and reactionary growth of the skin surface - this surface may eventually slough off revealing large ulcers prone to secondary infection. The disease is highly infectious and often fatal within three to five days. The life cycle is complex and will continue in the aquarium until all the fish are either dead or immune.

Amyloodinium. Also known as Coral Fish Disease. This is a rapidly progressing disease which starts off at the gills and so shows initially as respiratory distress but will then spread out across the skin. Signs include respiratory distress, skin rubbing and erratic swimming. Without treatment death will occur within two days of respiratory signs.

Brookynella and Uronema. Similar in appearance, these protozoa seem to be increasing in importance. The infections are initially confined to the gills but eventually will spread causing tissue irritation and skin slough producing ulcers. Fish become lethargic and secrete excess mucus. Death can occur within twelve hours from toxins released by the protozoa.

Cryptosporidium nasoris is a coccidian protozoan which attaches to the lining of the guts of naso tangs.Infected fish show emaciation, loss of appetite, regurgitation and droppings with undigested food in them. Other coccidia can invade the gall bladder, liver kidneys and even the gonads, effectively neutering the fish. Over sixty species of myxosporideal protozoa have been reported in marine fish. One particular one, Glugea heraldi, forms whitish cysts just under the skin on Atlantic seahorses.

Myxosporideal protozoa are another common infestation of wild caught marines.Indeed most tropical marines harbour Ceratomyxa, Myxidium or Leptotheca in their gallbladders. Septemcapsula plotosi has been found to infect the nervous tissue of coral catfish causing the fish to whirl before death.

Turbellarian flatworms have caused skin damage and eventual deaths in yellow tangs. Other species affected included surgeonfish, angelfish, butterflyfish, parrotfish and wrasse. Outbreaks are associated with poor husbandry and high levels of organic matter in the aquarium.

Monogenetic trematodes of the genera Gyrodactylus and Benedinia occasionally cause problems.Often near the eyes or gills, affected fish show signs of heavy respiration and scratch against objects in the aquarium. Some fish may hover in the water with their fins clamped tight against their body. The eyes may be inflamed - the tremetode Neobenedenia can cause corneal ulceration with eventual functional loss of the eye. Diseases caused by tapeworms and nematodes are relatively rare in aquaria, because in the majority of cases an intermediate host(s) is required in the worm's life cycle - a stage from which the fish will be isolated in the aquarium. Encysted stages or living worms may be found in fish. Some species may have an ability to switch to a direct life cycle - for instance Spirocamallanus which has been found in 16 species of tropical marine fish in Hawaiian waters, can prove to be a problem in aquarium fishes.

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Diseases due to Crustacea This group includes some "old favourites" such as the fish louse Argulus sp.which may occasionally turn up. Parasitic copepods may be seen, often near the eyes or gills. The isopod parasite Icthyotaces pteroisicola has been reported to cause marked skin swellings on the lionfish Pterois lunulata, each swelling acting as a protective sac for one parasite.

Nutritional Disorders. This is a vast subject. Very little is known of the nutritional requirements for the majority of marine fish. What is known is often extrapolated from those few, commercial species, which have been investigated. Having said that there are some very good proprietary flakes and the like available which at the very least provide a good basis for a nutritionally complete diet. Problems arise with those species not willing to take prepared foods. Examples of these are copperband butterfly fish which are primarily coral polyp predators - a diet difficult to provide in captivity; seahores require a constant availability of live foods such that if your brine shrimp culture fails they will quickly go into a negative energy balance; specialist predators such as sea bass and lionfish may suffer vitamin deficiencies if fed an unsupplemented fish only diet.

Head and Lateral Line Disease in tangs. Possibly a vitamin A deficiency manifesting if insufficiebt greens in diet..

High nitrite levels (F/water) 1 - 3 g/l salt indefinitely.

Lymphocystis No direct cure.Ozone or UV may reduce spread.

Tang Fingerprint Disease No known cure.

Infectious Pancreatic Necrosis No known cure.

Angelfish Encephalitis No known cure.

Bacterial diseases Antibiotics required,culture and sensitivity testing. Chloramine-T @ 10mg/l - use less in soft water, down to 2mg/l.

Fish TB Antibiotic treatment not very effective. Consider euthanasia especially because of slight risk to people.

Epitheliocystis Difficult - consider chloramphenicol or enrofloxacin.

Exophialiosis No effective treatment

Ichthyophonus No effective treatment.

White Spot (Icthyophthirius) Use proprietary medication

Cryptocaryon irritans Sensitive to copper-based treatments.

Chilonodella, Trichodina and Tetrahymena Proprietary medications or glacial acetic acid dips @ 8mls per gallon for 30-45 seconds. May kill weak fish.

Amyloodinium ocellatum Sensitive to copper-based treatments.

Oodinium Metronidazole @ 50mg/l for up to 24hrs daily for 10 days, or Quinine hydrochloride @ 10-20mg/l indefinitely. Some fish sensitive.

Brooklynella and Uronema Sensitive to copper-based treatments.

Ichthyobodo necatrix Usual ciliate treatments

Microsporidians No known cure.

Myxosporideans No known cure.

Turbellaria Formalin bath at 2 ml formalin per litre for up to 1 hour; 5 mins freshwater bath daily for 5 days.

Monogenetic trematodes Freshwater dips (marine species); or praziquantel bath at 10mg/l for up to 3 hours.

Nematodes Levamisol at 2mg/l for up to 24 hrs. Benzimidazoles eg. Fenbendazole @ 20mg/kg bodyweight given 7 days apart, or Mebendazole @ 20mg/kg for 3 treatments given @ weekly intervals.

Cestodes. Praziquantel @10mg/l for a 3 hour bath.

Crustacea Individual removal of parasites, or treat with dichlorvos @ 1ppm for 1 hour.

In all cases the maintenance of optimum environmental conditions is the best adjunct to treatment.NEVER use copper based treatments in aquaria containing invertebrates and ideally always use a separate dedicated treatment aquarium.